The present invention relates generally to air towers used in refrigeration appliances with a top mount freezer.
A common air circulation arrangement for refrigeration appliances with top mount freezers is to have an air tower located generally at the rear of the refrigeration compartments to guide a flow of chilled air into an upper and a lower refrigeration compartment. For example, U.S. Pat. No. 5,369,963 discloses an air tower construction for use in a top mount freezer refrigeration appliance. Air towers are also disclosed in U.S. Pat. Nos. 4,920,765 and 5,735,138. Air is directed over an evaporator to chill the air, usually well below 0° C. (32 ° F.) and the chilled air is directed into the air tower to diffuse into the freezer compartment and into the fresh food compartment, at a determined ratio, so that a temperature differential is maintained in the two compartments. Since the air in the tower is usually at a temperature well below the freezing temperature of water, there is a noticeable ice and moisture buildup on the air tower when the product is run in humid conditions. This moisture buildup is due to the fact that moisture from the atmosphere is attracted to the coldest surfaces in the two compartments, such as the evaporator cover and the air tower.
In order to remove ice build up in the freezer compartment, it is known to utilize defrost cycles in which a heater is used to warm the area, particularly associated with the evaporator, at various intervals, such as described in U.S. Pat. No. 3,727,419, so that the user is not required to periodically deenergize the freezer, remove all of the food items, and allow the ice to melt. However, due to the low thermal conductivity of the plastic material normally used for the air tower, all of the frost and ice build-up is not melted from the tower during defrost cycles. This has lead to a significant number of customer complaints and service calls, to remove the ice build up on the air tower, which can restrict the flow of air into the two compartments, and alter the ratio of cold air flowing to the two compartments, thereby altering the preset temperature differential.
It would be an improvement in the art if air towers were provided with a means of reducing the ice build up associated with the air tower, or to enhance the ice removal during defrost cycles.